The present invention relates to organometallic compounds a to catalyst systems for the polymerization of olefins comprising such organometallic compounds. The invention also relates to a process for the polymerization of olefins carried out in the presence of the above catalyst system.
Homogeneous catalytic systems based on metallocene complexes are known to be active in the polymerization of olefins; said complexes must be activated by means of suitable cocatalytic compounds.
The first generation of cocatalysts developed for homogeneous metallocene olefin polymerization consisted of alkyl aluminum chlorides (AlR5Cl), wherein substituents R are preferably methyl or ethyl; these cocatalysts exhibit low ethylene polymerization activity levels and negligible propylene polymerization activity.
The second generation of cocatalyst systems comprised the class of alkylalumoxanes, commonly obtained by reacting trialkyl aluminum compound and water in a molar ratio of 1:1 to 100:1; these alumoxanes are oligomeric linear and/or cyclic compounds represented by the formulae: 
for linear oligomeric alumoxanes, and 
for cyclic oligomeric alumoxanes, wherein the substituents R are usually methyl, ethyl or isobutyl groups, n ranges from 0 to 40, and m ranges from 3 to 40. Methylalumoxane (MAO) is the most widely used cocatalyst.
Nevertheless alkylalumoxanes, and in particular methylalumoxane, though very active in metallocene-based catalyst systems, exhibit several inherent problems in use, such as the need for high alumoxane/metallocene molar ratios to produce satisfactory catalytic activities, their high reactivity toward impurities (moisture, alcohols etc.) and their easy flammability. Moreover, it has not been possible to isolate characterizable metallocene active species using MAO. Accordingly, some of the developments in this area involved a search for alternative cocatalysts. B(C6F5)4xe2x88x92 types of non-coordinating anions have been developed as cocatalysts for metallocene-based systems. More specifically, these activators are ion-exchange compounds comprising a trialkyl or dialkylammonium cation, which will irreversibly react with a metallocene, and a fluorinated arylborate anion, capable of stabilizing the metallocene cation complex and sufficiently labile to permit displacement by ethylene during polymerization (see for instance WO 91/02012). In particular, they have the advantage of being used in a 1:1 catalyst-cocatalyst ratio. Therefore, it is usually not necessary to remove the small amount of boron from the final polymer, unlike the aluminum-based cocatalysts mentioned above. As preferred activators are tri(n-butyl)ammonium tetrakis(pentafluorophenyl)boron and N,N-dimethylanilinium tetrakis(pentafluorophenyl)boron.
These cocatalysts exhibit high catalytic activities but, from a synthetic point of view, the industrial production of these cocatalysts is quite expensive.
Finally, these B(C6F5)4xe2x88x92 anions are generally used in the form of the corresponding ammonium salts, thus leading to the release of aminic by-products in consequence of the metallocene activation. In addition they have a low solubility in the polymerization solvents.
The fourth generation of cocatalysts is B(C6F5)3. The anion MeB(C6F5)3xe2x88x92 formed after Mexe2x88x92 abstraction from the metallocene dimethyl complex is weakly coordinated to the electrondeficient metal center, thus resulting in a decrease of the catalytic activity and in addition the catalyst system is not stable.
An alternative route for using B(C6F5)3 has been proposed by B. Temme in Journal of Organometallic Chemistry 488 (1995) 177-182. Bis cyclopentadienyl methyl pyrrolidyl zirconocene has been treated with B(C6F5)3 with the formation of the pyrrolydyl borate and the metallocene cation. In this paper it is reported that the obtained salt is catalytically active and polymerizes ethylene even if with a moderate activity.
WO 99/64476 describes a process for the preparation of polyolefins by using a catalyst system comprising a metallocene compound, a Lewis acid-base complex and a tri-n-alkylaluminum compound. As described at page 4 and illustrated in the figures the function of the Lewis base is to inhibit the reaction between the metallocene compounds and the Lewis acid. Only upon addition of the tri-n-alkylaluminum compound the catalyst system becomes active. This catalyst system does not solve completely the problems of the use B(C6F5)3, for the reason that the anion that is weakly coordinated to the electrondeficient metal center is always of the type MeB(C6F5)3xe2x88x92 and therefore the active catalyst system is not stable for a long time.
Therefore, there is still the need for alternative cocatalysts, easy to prepare, that form a stable catalyst system and able to exert good activities in the polymerization of olefins.
The Applicant has now found a new class of olefin polymerization cocatalysts, which reduces the use of excess of cocatalyst with respect to alkylaluminoxanes, does not lead to the release of undesired by-products after the metallocene activation, and provides stable catalytic compositions.
The present invention concerns an organometallic compound obtainable by contacting
a) a compound having the following formula (I): 
wherein Ra, Rb, Rc and Rd equal to or different from each other are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated, C1-C10 alkyl, C6-C20 aryl, C7-C20 arylalkyl and C7-C20 alkylaryl groups, optionally containing O, S, N, P, Si or halogen atoms, or two or more adjacent substituents Ra, Rb, Rc and Rd form one or more C4-C7 rings, optionally containing O, S, N, P or Si atoms, that can bear substituents; with
b) a Lewis acid of formula (II)
MtR13 xe2x80x83xe2x80x83(II)
wherein Mt is a metal belonging to Group 13 of the Periodic Table of the Elements (IUPAC); R1, equal to or different from each other, are selected from the group consisting of halogen, halogenated C6-C20 aryl and halogenated C7-C20 alkylaryl groups; two R1 groups can also form with the metal Mt one condensed ring, such as for example 9-borafluorene compounds.
Preferably Mt is B or Al, and more preferably is B; The substituents R1 are preferably selected from the group consisting of C6F5, C6F4H, C6F3H2, C6H3(CF3)2, perfluoro-biphenyl, heptafluoro-naphthyl, hexafluoro-naphthyl and pentafluoro-naphthyl; Most preferred R1 substituents are C6F5 radicals.
Preferred organometallic compounds are those belonging to the following two classes (1) and (2), having respectively formula (III) and (IV).
Class (1)
Organometallic compounds belonging to class (1) have the following formula (III) 
wherein
Mt is a metal belonging to Group 13 of the Periodic Table of the Elements (IUPAC); R1, equal to or different from each other, are selected from the group consisting of halogen, halogenated C6-C20 aryl and halogenated C7-C20 alkylaryl groups; two R1 groups can also form with the metal Mt one condensed ring, such as for example 9-borafluorene compounds; and the substituents R5, R4, R3 and R2 equal to or different from each other, are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated, C1-C10 alkyl, C6-C20 aryl, C7-C20 arylalkyl and C7-C20 alkylaryl groups, optionally containing O, S, N, P, Si or halogen atoms, or two or more adjacent substituents R2-R5 form one or more C4-C7 rings, optionally containing O, S, N, P or Si, preferably when the substituents R2-R5 form one or more rings, R4 and R5 form one C4-C7 aromatic ring, optionally containing O, S, N, or P atoms, that can bear substituents; and R2 and R3 form one non aromatic C4-C7 ring, optionally containing O, S, N, P or Si atoms; with the proviso that at least one of R2, R3, R4 and R5is different from hydrogen.
Preferably in the organometallic compounds of formula (III) Mt is B or Al, and more preferably is B; the substituents R1 equal to or different from each other, are preferably selected from the group consisting of C6F5, C6F4H, C6F3H2, C6H3(CF3)2, perfluoro-biphenyl, heptafluoro-naphthyl, hexafluoro-naphthyl and pentafluoro-naphthyl; even more preferably, R1 is C6F5; at least one of the substituents R5 and R4 are preferably a C6-C20 aryl, C7-C20 arylalkyl and C7-C20 alkylaryl groups, optionally containing O, S, N P, Si or halogen atoms or together they can form an aromatic C4-C7 ring optionally containing O, S, N or P atoms, that can bear substituents.
A preferred subclass of organometallic compounds of formula (III) is that of formula (V): 
wherein
B is a boron atom;
the substituents R1, R3 and R2 have the meaning reported above and the substituents R6, the same or different from each other, are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated, C1-C10 alkyl, C6-C20 aryl, C7-C20 arylalkyl and C7-C20 alkylaryl groups optionally containing O, S, N, P, Si or halogen atoms, or two or more adjacent substituents R6 form one or more C4-C7 optionally containing O, S, N, P or Si atoms rings that can bear substituents; preferably R6 are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated C1-C10 alkyl. Preferably R2 and R3 are hydrogen. Another preferred subclass of organometallic compounds of formula (III) is that of formula (VI): 
wherein the substituents R1 and R6 have the meaning reported above.
Class (2)
Organometallic compound belonging to class (2) have the following formula (IV): 
wherein
Mt and R1 are defined as above;
the substituents R2xe2x80x2, R3xe2x80x2, R4xe2x80x2 and R5xe2x80x2 equal to or different from each other, are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated, C1-C10 alkyl, C6-C20 aryl, C7-C20 arylalkyl and C7-C20 alkylaryl groups, optionally containing O, S, N, P, Si or halogen atoms, or two or more adjacent substituents R2xe2x80x2, R3xe2x80x2, R4xe2x80x2 and R5xe2x80x2 form one or more C4-C7 rings optionally containing O, S, N, P or Si atoms, that can bear substituents; said rings can be aliphatic or optionally can contain double bonds, with the proviso that said rings are not aromatic.
Preferably the substituents R2xe2x80x2, R3xe2x80x2, R4xe2x80x2 and R5xe2x80x2 equal to or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated, C1-C10 alkyl, optionally containing O, S, N, P, Si or halogen atoms, or two or more adjacent substituents R2xe2x80x2, R3xe2x80x2, R4xe2x80x2 and R5xe2x80x2 form one or more C4-C7 rings optionally containing O, S, N, P or Si atoms, that can bear substituents; said rings can be aliphatic or optionally can contains double bonds, with the proviso that said rings are not aromatic;
A preferred subclass of organometallic compounds of formula (IV) is that of formula (VII): 
wherein
the substituents R1 have the meaning described above and the substituents R2xe2x80x2 and R5xe2x80x2 equal to or different from each other are C1-C20 alkyl; preferably they are methyl or ethyl groups.
Non limitative examples of compounds belonging to formula (I) are:
pyrrole; ethyl 3,5-dimethyl-2-pyrrolecarboxylate; tert-butyl 3,4,5-trimethyl-2-pyrrole carboxylate; ethyl 3, 4-diethyl-5-methyl-2-pyrrole carboxylate; tert-butyl 4-acetyl-3,5 dimethyl-2-pyrrole carboxylate; diethy 3,4-pyrroledicarboxylate; 2-ethylpyrrole; 2,4-dimethylpyrrole; 2,5-dimethylpyrrole; 4,5,6,7-tetrahydroindole; 1,2,5-trimethylpyrrole; 2,4-dimethyl-3-ethylpyrrole; 3-acetyl-2,4-dimethylpyrrole; 3-ethyl-2-methyl-1,5,6,7-tetrahydro-4-H-indol-4-one; 2-acetylpyrrole; 2-(trichloroacetyl)pyrrole; 1,5,6,7-tetrahydro-4h-indol-4-one; 2-(trifluoroacetyl)pyrrole; pyrrole-2-carboxaldehyde; indole; 2-methylindole; 3-methylindole; 4-methylindole; 5-methylindole; 6-methylindole; 7-methylindole; 2,3-dimethylindole; 2,5-dimethylindole; 5-fluoroindole; 4-chloroindole; 5-chloroindole; 6-chloroindole; 5-chloro-2-methylindole; 5-bromoindole; 5-methoxyindole; 4-methoxyindole; 5-acetoxy-2-methylindole; 5,6-dimethoxyindole; 5-benzyloxyindole; 4-nitroindole; 5-nitroindole; 3-acetylindole; 3-(trifluoroacetyl)indole; indole-3-carboxyaldehyde; 2-methylindole-3-carboxyaldehyde; 5-methoxyindole-3-carboxyaldehyde; phenyl-3,3xe2x80x2-dimethyl-2,2xe2x80x2-diindolyl-methane, 3-indolyl acetate; 4-indolyl acetate; methyl indole-4-carboxylate; methyl 4-methoxy-2-indolecarboxylate; 3-cyanoindole; 5-cyanoindole; 7-azaindole.
Example of Lewis acid of formula (II) are:
tris(pentafluorophenyl)borane;tris(heptafluoronaphthyl)borane; tris(2,3,5,6,7,8-hexafluoronaphthyl)borane; tris(2,4,5,6,7,8-hexafluoronaphthyl)borane; tris(3,4,5,6,7,8-hexafluoronaphthyl)borane; tris(2,3,4,6,7,8-hexafluoronaphthyl)borane; tris(2,3,4,5,7,8-hexafluoronaphthyl)borane; tris(2,3,5,6,7,8-hexafluoro-4-methylnaphthyl)borane; tris(2,4,5,6,7,8-hexafluoro-3-methylnaphthyl)borane; tris(3,4,5,6,7,8-hexafluoro-2-methylnaphthyl)borane; tris(2,3,4,6,7,8-hexafluoro-5-methylnaphthyl)borane; tris(2,3,4,5,7,8-hexafluoro-6-methylnaphthyl)borane; tris(nonafluorobiphenyl)borane; tris(2,2xe2x80x2,3,3xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluorobiphenyl)borane; tris(3,3xe2x80x2,4,4xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluorobiphenyl)borane; tris(2,2xe2x80x2,4,4xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluorobiphenyl)borane; tris(2,2xe2x80x2,3,3xe2x80x2,4,4xe2x80x2,6,6xe2x80x2-octafluorobiphenyl)borane; tris(2,2xe2x80x2,3,3xe2x80x2,4,4xe2x80x2,5,5xe2x80x2-octafluorobiphenyl)borane; tris(2,2xe2x80x2,3,3xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluorobiphenyl)borane; tris(3,3xe2x80x2,4,4xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluorobiphenyl)borane; tris(2,2xe2x80x2,4,4xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluorobiphenyl)borane; tris(2,2xe2x80x2,3,3xe2x80x2,4,4xe2x80x2,6,6xe2x80x2-octafluoro-5,5xe2x80x2-methylbiphenyl)borane; tris(2,2xe2x80x2,3,3xe2x80x2,4,4xe2x80x2,5,5xe2x80x2-octafluoro-6,6xe2x80x2-methylbiphenyl)borane; tris(2,2xe2x80x2,3,3xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluoro-4,4xe2x80x2-biphenyl)borane; tris(3,3xe2x80x2,4,4xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluoro-2,2xe2x80x2-biphenyl)borane; tris(2,2xe2x80x2,4,4xe2x80x2,5,5xe2x80x2,6,6xe2x80x2-octafluoro-3,3xe2x80x2-biphenyl)borane; tris(2,3,4,6-tetrafluorophenyl)borane; tris(2,3,5,6-tetrafluorophenyl)borane; tris(2,3,5-trifluorophenyl)borane, tris(2,3,6-trifluorophenyl)borane; tris(1,3-difluorophenyl)borane, tris(2,3,5,6-tetrafluoro-4-methylphenyl)borane; tris(2,3,4,6-tetrafluoro-5-methylphenyl)borane; tris(2,6-difluoro-3-methylphenyl)borane; tris(2,4-difluoro-5-methylphenyl)borane; tris(3,5-difluoro-2-methylphenyl)borane; fluorobis(pentafluorophenyl)borane; chlorobis(pentafluorophenyl)borane; dichloro(pentafluorophenyl)borane; difluoro (pentafluorophenyl)borane; 9-chloro-9-boroperfluorofluorene; 9-methyl-9-boroperfluorpfluorene; 9-pentafluorophenyl-9-oroperfluorofluorene and 9-bromo-9-boroperfluorofluorene.
It is another object of the present invention a catalyst system for the polymerization of olefins comprising the product obtained by contacting:
(A) at least one transition metal organometallic compound, pyrrolidyl bis(xcex7- cyclopentadienyl)methylzirconium being excluded and,
(B) an organometallic compound obtainable by contacting
a) a compound having the following formula (I): 
wherein Ra, Rb, Rc and Rd equal to or different from each other are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated, C1-C10 alkyl, C6-C20 aryl, C7-C20 arylalkyl and C7-C20 alkylaryl groups, optionally containing O, S, N, P, Si or halogen atoms, or two or more adjacent substituents Ra, Rb, Rc and Rd form one or more C4-C7 rings, optionally containing O, S, N, P or Si atoms, that can bear substituents; with
b) a Lewis acid of formula (II)
MtR13 xe2x80x83xe2x80x83(II)
wherein Mt is a metal belonging to Group 13 of the Periodic Table of the Elements (IUPAC); R1, equal to or different from each other, are selected from the group consisting of halogen, halogenated C6-C20 aryl and halogenated C7-C20 alkylaryl groups; two R1 groups can also form with the metal Mt one condensed ring, such as for example 9-borafluorene compounds; and
(C) optionally an alkylating agent.
Preferably the catalyst system for the polymerization of olefins comprises the product obtained by contacting:
(A) at least one transition metal organometallic compound, pyrrolidyl bis(xcex7- cyclopentadienyl)methylzirconium being excluded;
(B) an organometallic compound belonging to class (1) (compounds of formula (III), (V), and (VI)) or class (2) (compounds of formula (IV) and (VII)) as described above; and
(C) optionally an alkylating agent.
Transition metal organometallic compounds for use in the catalyst system in accordance with the present invention are compounds suitable as olefin polymerization catalysts by coordination or insertion polymerization. The class includes known transition metal compounds useful in traditional Ziegler-Natta coordination polymerization, the metallocene compounds similarly and the late transition metal compounds known to be useful in coordination polymerization. These will typically include Group 4-10 transition metal compounds wherein at least one metal ligand can be abstracted by the catalyst activators. As a rule, when said ligand is hydrogen or an hydrocarbyl group containing from 1 to 20 carbon atoms optionally containing silicon atoms, the transition metal organometallic catalyst compounds can be used as such, otherwise an alkylating agent has to be used in order to alkylate said catalyst. The alkylation can be carried out in a separate step or in situ.
The alkylating agent is a compound able to react with the transition metal organometallic catalyst compounds and exchange said ligand that can be abstracted, with an alkyl group. Preferably said alkylating agent is selected from the group consisting of R10Li, R10Na, R10K, R10MgU or AlR103xe2x88x92zWz, or alumoxanes, wherein R10 can be C1-C10 alkyl, alkenyl or alkylaryl radicals, optionally containing one or more Si or Ge atoms, z is 0, 1 or 2 or a non integer number ranging from 0 to 2; U is chlorine, bromine or iodine and W is hydrogen or chlorine, bromine or iodine atom; non-limiting examples of R10 are methyl, ethyl, butyl and benzyl; non limiting example of AlR103xe2x88x92zWz compounds are trimethylaluminum (TMA), tris(2,4,4-trimethyl-pentyl)aluminum (TIOA), tris(2-methyl-propyl)aluminum (TIBA), tris(2,3,3-trimethyl-butyl)aluminum, tris(2,3-dimethyl-hexyl)aluminum, tris(2,3-dimethyl-butyl)aluminum, tris(2,3-dimethyl-pentyl)aluminum, tris(2,3-dimethyl-heptyl)aluminum, tris(2-methyl-3-ethyl-pentyl)aluminum and tris(2-ethyl-3,3-dimethyl-butyl). Non limiting example of alumoxanes are: methylalumoxane (MAO), tetra-(isobutyl)alumoxane (TIBAO), tetra-(2,4,4-trimethyl-pentyl)alumoxane (TIOAO), tetra-(2,3 -dimethylbutyl)alumoxane (TDMBAO) and tetra-(2,3,3-trimethylbutyl)alumoxane (TTMBAO).
Different from the catalyst system disclosed in WO 99/64476, the catalyst system of the present invention is stable and can be isolated.
A preferred class of transition metal organometallic compounds are metallocene compounds belonging to the following formula (VIII)
(Cp)(ZR7m)n(A)rMLpxe2x80x83xe2x80x83(VIII)
wherein (ZR7m)n is a divalent group bridging Cp and A; Z being C, Si, Ge, N or P, and the R7 groups, equal to or different from each other, being hydrogen or linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl groups or two R7 can form a aliphatic or aromatic C4-C7 ring;
Cp is a substituted or unsubstituted cyclopentadienyl group, optionally condensed to one or more substituted or unsubstituted, saturated, unsaturated or aromatic rings, containing from 4 to 6 carbon atoms, optionally containing one or more heteroatoms;
A is O, S, NR8, PR8 wherein R8 is hydrogen, a linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl, or A has the same meaning of Cp;
M is a transition metal belonging to group 4, 5 or to the lanthanide or actinide groups of the Periodic Table of the Elements (IUPAC version);
the substituents L, equal to or different from each other, are monoanionic sigma ligands selected from the group consisting of hydrogen, halogen, R9, OR9, OCOR9, SR9, NR92 and PR92. wherein R9 is a linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl group, optionally containing one or more Si or Ge atoms; preferably, the substituents L are the same;
m is 1 or 2, and more specifically it is 1 when Z is N or P, and it is 2 when Z is C, Si or Ge;
n is an integer ranging from 0 to 4;
r is 0, 1 or 2; preferably 0 or 1; n is 0 when r is 0;
p is an integer equal to the oxidation state of the metal M minus r+1; i.e. minus 3 when r=2, minus 2 when r=1, and minus 1 when r=0, and ranges from 1 to 4.
In the metallocene compound of formula (VIII), the divalent bridge (ZR7m)n is preferably selected from the group consisting of CR72, (CR72)2, (CR72)3, SiR72, GeR72, NR7 and PR7, R7 having the meaning reported above; more preferably, said divalent bridge is Si(CH3)2, SiPh2, CH2, (CH2)2, (CH2)3 or C(CH3)2.
The variable m is preferably 1 or 2; the variable n ranges preferably from 0 to 4 and, when n greater than 1, the atoms Z can be the same or different from each other, such as in divalent bridges CH2xe2x80x94O, CH2xe2x80x94S and CH2xe2x80x94Si(CH3)2.
The ligand Cp, which is xcfx80-bonded to said metal M, is preferably selected from the group consisting of cyclopentadienyl, mono-, di-, tri- and tetra-methyl cyclopentadienyl; 4-tbutyl-cyclopentadienyl; 4-adamantyl-cyclopentadienyl; indenyl; mono-, di-, tri- and tetra-methyl indenyl; 2-methyl indenyl, 3-tbutyl-indenyl, 4-phenyl indenyl, 4,5 benzo indenyl; 3-trimethylsilyl-indenyl; 4,5,6,7-tetrahydroindenyl; fluorenyl; 5,10-dihydroindeno[1,2-b]indol-10-yl; N-methyl- or N-phenyl-5,10-dihydroindeno [1,2-b]indol-10-yl; 5,6-dihydroindeno[2,1-b]indol-6-yl; N-methyl-or N-phenyl-5,6-dihydroindeno[2,1-b]indol-6-yl; azapentalene-4-yl; thiapentalene-4-yl; azapentalene-6-yl; thiapentalene-6-yl; mono-, di- and tri-methyl-azapentalene-4-yl, 2,5-dimethyl-cyclopenta[1,2-b :4,3-bxe2x80x2]-dithiophene.
The group A is O, S, N(R8), wherein R8 is hydrogen, a linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl, preferably R8 is methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, phenyl, p-n-butyl-phenyl, benzyl, cyclohexyl and cyclododecyl; more preferably R8 is t-butyl; or A has the same meaning of Cp.
Non limiting examples of compounds belonging to formula (VIII) are the rac and meso form (when present) of the following compounds:
bis(cyclopentadienyl)zirconium dimethyl;
bis(indenyl)zirconium dimethyl;
bis(tetrahydroindenyl)zirconium dimethyl;
bis(fluorenyl)zirconium dimethyl;
(cyclopentadienyl)(indenyl)zirconium dimethyl;
(cyclopentadienyl)(fluorenyl)zirconium dimethyl;
(cyclopentadienyl)(tetrahydroindenyl)zirconium dimethyl;
(fluorenyl)(indenyl)zirconium dimethyl;
dimethylsilanediylbis(indenyl)zirconium dimethyl,
dimethylsilanediylbis(2-methyl-4-phenylindenyl)zirconium dimethyl,
dimethylsilanediylbis(4-naphth ylindenyl)zirconium dimethyl,
dimethylsilanediylbis(2-methylindenyl)zirconium dimethyl,
dimethylsilanediylbis(2-methyl4-t-butylindenyl)zirconium dimethyl,
dimethylsilanediylbis(2-methyl-4-isopropylindenyl)zirconium dimethyl,
dimethylsilanediylbis(2,4-dimeth ylindenyl)zirconium dimethyl,
dimethylsilanediylbis(2-methyl-4,5-benzoindenyl)zirconium dimethyl,
dimethylsilanediylbis(2,4,7-trimethylindenyl)zirconium dimethyl,
dimethylsilanediylbis(2,4,6-trimethylindenyl)zirconium dimethyl,
dimethylsilanediylbis(2,5,6-trimethylindenyl)zirconium dimethyl,
methyl(phenyl)silanediylbis(2-methyl-4,6-diisopropylindenyl)-zirconium dimethyl,
methyl(phenyl)silanediylbis(2-methyl-4-isopropylindenyl)-zirconium dimethyl,
1,2-ethylenebis(indenyl)zirconium dimethyl,
1,2-ethylenebis(4,7-dimethylindenyl)zirconium dimethyl,
1,2-ethylenebis(2-methyl-4-phenylindenyl)zirconium dimethyl,
1,4-butanediylbis(2-methyl-4-phenylindenyl)zirconium dimethyl,
1,2- ethylenebis(2-methyl-4,6-diisopropylindenyl)zirconium dimethyl,
1,4-butanediylbis(2-methyl-4-isopropylindenyl)zirconium dimethyl,
1,4-butanediylbis(2-methyl-4,5-benzoindenyl)zirconium dimethyl,
1,2- ethylenebis (2-methyl-4,5-benzoindenyl)zirconium dimethyl,
[4-(xcex75-cyclopentadienyl)-4,6,6-trimethyl(xcex75-4,5-tetrahydropentalene)]dimethylzirconium,
[4-(xcex75-3xe2x80x2-trimethylsilylcyclopentadienyl)-4,6,6-trimethyl(xcex75-4,5-tetrahydropentalene)]dimethylzirconium,
(tert-butylamido)(tetramethyl-xcex75-cyclopentadienyl)-1,2-ethanedimethyltitanium,
(methylamido)(tetramethyl-xcex75-cyclopentadienyl)dimethylsilyldimethyltitanium,
(methylamido)(tetramethyl-xcex75-cyclopentadienyl)-1,2-ethanediyldimethyltitanium,
(tertbutylamido)-(2,4-dimethyl-2,4-pentadien-1-yl)dimethylsilyldimethyltitanium,
bis(1,3-dimethylcyclopentadienyl)zirconium dimethyl,
methylene(3-methyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl;
methylene(3-isopropyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene(2,4-dimethyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene(2,3,5-trimethyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene-1-(indenyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene-1-(indenyl)-7-(2,5-ditrimethylsilylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene-1-(3-isopropyl-indenyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene- 1-(2-methyl-indenyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene-1-(tetrahydroindenyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
methylene(2,4-dimethyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dioxazol)zirconium dimethyl and dimethyl;
methylene(2,3, 5-trimethyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dioxazol)zirconium dimethyl and dimethyl;
methylene-1-(indenyl)-7-(2,5-dimethylcyclopentadienyl-[1 ,2-b:4,3-bxe2x80x2]dioxazol)zirconium dimethyl and dimethyl;
isopropylidene(3-methyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b: 4,3 -bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
isopropylidene(2,4-dimethyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b: 4,3 -bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
isopropylidene(2,4-diethyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
isopropylidene(2,3,5-trimethyl-cyclopentadienyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3-bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
isopropylidene-1-(indenyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3 -bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
isopropylidene-1-(2-methyl-indenyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b :4,3 -bxe2x80x2]dithiophene)zirconium dimethyl and dimethyl;
dimethylsilandiyl- 1-(2-methyl-indenyl)-7-(2,5-dimethylcyclopentadienyl-[1,2-b:4,3 -bxe2x80x2]dithiophene)hafnium dimethyl and dimethyl;
dimethylsilanediyl(3-tert-butyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
dimethylsilanediyl(3-isopropyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
dimethylsilanediyl(3-methyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
dimethylsilanediyl(3-ethyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
1-2-ethane(3-tert-butyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
1-2-ethane (3-isopropyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
1-2-ethane (3-methyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
1-2-ethane (3-ethyl-cyclopentadienyl)(9-fluorenyl)zirconium dimethyl,
dimethylsilandiylbis-6-(3-methylcyclopentadienyl-[1,2-b]-thiophene) dimethyl;
dimethylsilandiylbis-6-(4-methylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(4-isopropylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(4-ter-butylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium di methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[ 1,2-b]-thiophene]zirconium dimethyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-thiophene]zirconium dimethyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-thiophene]zirconium dimethyl;
dimethylsilandiylbis-6-(2,4,5 -trimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dimethyl;
dimethylsilandiylbis-6-(3-methylcyclopentadienyl-[1,2-b]-silole)zirconium dimethyl;
dimethylsilandiylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-silole)zirconium dimethyl;
dimethylsilandiylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dimethyl;
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dimethyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-silole]zirconium dimethyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-silole]zirconium dimethyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-silole]zirconium dimethyl;
dimethylsilandiylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dimethyl;
[dimethylsilyl(tert-butylamido)][(N-methyl- 1 ,2-dihydrocyclopenta[2,1-b]indol-2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(6-methyl-N-methyl-1,2-dihydrocyclopenta[2,1-b]indol-2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(6-methoxy-N-methyl-1,2-dihydrocyclopenta[2,1-b]indol-2-yl)]titanium dimethyl;
[dimetbylsilyl(tert-butylamido)][(N-ethyl-1,2-dihydrocyclopenta[2,1-b]indol-2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(N-phenyl- 1,2-dihydrocyclopenta[2,1-b]indol2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(6-methyl-N-phenyl- 1,2-dihydrocyclopenta[2,1-b]indol2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(6-methoxy-N-phenyl- 1,2-dihydrocyclopenta[2,1-b]indol2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(N-methyl-3,4-dimethyl- 1 ,2-dihydrocyclopenta[2,1-b]indol-2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(N-ethyl-3,4-dimethyl-1,2-dihydrocyclopenta[2,1-b]indol-2-yl)]titanium dimethyl;
[dimethylsilyl(tert-butylamido)][(N-phenyl-3,4-dimethyl-1,2-dihydroclopenta[2,1-b]indol-2-yl)]titanium dimethyl;
as well as the corresponding dichloro, hydrochloro and dihydro compounds and the corresponding xcex74-butadiene compounds.
When A is N(R8), a suitable class of metallocene complexes (A) for use in the catalysts complexes of the invention comprises the well-known constrained geometry catalysts, as described in EP-A-0 416 815, EP-A-0 420 436, EP-A-0 671 404, EP-A-0 643 066 and WO-A-91/04257.
According to a preferred embodiment of the invention, the group A has the same meaning of Cp, and is preferably substituted or unsubstituted cyclopentadienyl, indenyl, tetrahydroindenyl (2,5-dimethyl-cyclopenta[1,2-b:4,3-bxe2x80x2]-dithiophene).
Suitable metallocene complexes that may be used in the catalyst system according to the present invention are described in WO 98/22486, WO 99/58539 WO 99/24446, U.S. Pat. No. 5,556,928, WO 96/22995, EP-485822, EP-485820, U.S. Pat. No. 5,324,800 and EP-A-0 129 368.
The metal M is preferably Ti, Zr or Hf, and more preferably Zr.
The substituents L are preferably the same and are selected from the group consisting of halogens, R9, OR9 and NR92; wherein R9 is a C1-C7 alkyl, C6-C14 aryl or C7-C14 arylalkyl group, optionally containing one or more Si or Ge atoms; more preferably, the substituents L are selected from the group consisting of xe2x80x94Cl, xe2x80x94Br, xe2x80x94Me, xe2x80x94Et, xe2x80x94n-Bu, xe2x80x94sec-Bu, xe2x80x94Ph, xe2x80x94Bz, xe2x80x94CH2SiMe3, xe2x80x94OEt, xe2x80x94OPr, xe2x80x94OBu, xe2x80x94OBz and xe2x80x94NMe2, even more preferably L is methyl.
The integer n ranges from 0 to 4, and it is preferably 1 or 2.
When n=0 and r=1, A can have only the meaning of Cp; Cp and A are preferably pentamethyl cyclopentadienyl, indenyl or 4,5,6,7-tetrahydroindenyl groups.
Non-limiting examples of these metallocene complexes are:
and the corresponding xe2x80x94MMe2, xe2x80x94M(OMe)2, xe2x80x94MH2, xe2x80x94MHCl, xe2x80x94MMeOMe, xe2x80x94MmeOEt, xe2x80x94MMeOCH2Ph, xe2x80x94MMeOPh xe2x80x94M(OEt)2, xe2x80x94MCl(OMe), xe2x80x94MCl(OEt), xe2x80x94MPh2, xe2x80x94MBz2, xe2x80x94MMeCl, xe2x80x94MPhCl, xe2x80x94M(NMe2)2 and xe2x80x94M(NMe2)OMe derivatives, wherein Me=methyl, Et=ethyl, Cp=cyclopentadienyl, Ind=indenyl, H4Ind=4,5,6,7-tetrahydroindenyl, Ph=phenyl, Bz=benzyl, and M is preferably Zr.
When n=1 or 2 and r=1, Cp and A, same or different from each other, are preferably cyclopentadienyl, tetramethyl-cyclopentadienyl, indenyl, 4,5,6,7-tetra-hydro-indenyl, 2-methyl-4,5,6,7-tetra-hydro-indenyl, 4,7-dimethyl4,5,6,7-tetra-hydroindenyl, 2,4,7-trimethyl-4,5,6,7-tetra-hydro-indenyl or fluorenyl groups; (ZR7m)n is preferably Me2Si, Me2C, CH2 or C2H4. Non-limiting examples of metallocene complexes of formula (II), wherein n=1 or 2 and r=1, are:
and the corresponding xe2x80x94MMe2, xe2x80x94M(OMe)2, xe2x80x94M(OEt)2, xe2x80x94MCl(OMe), xe2x80x94MCl(OEt), xe2x80x94MPh2, xe2x80x94MBz2, xe2x80x94MMeCl, xe2x80x94MPhCl, xe2x80x94M(NMe2)2 and xe2x80x94M(NMe2)OMe derivatives, wherein Me, Cp, Ind, Flu, Ph, Bz, H4Ind and M has the meanings reported above.
Suitable metallocene complexes (A) are the bridged bis-indenyl metallocenes as described for instance in U.S. Pat. No. 5,145,819 and EP-A-0 485 823.
Further metallocene complexes suitable for the catalyst system of the invention are the classes of heterocyclic metallocenes described in WO 98/22486 and WO 99/24446. Among these metallocenes, particularly preferred are the ones reported from page 15, line 8 to page 24, line 17; from page 25, line 1 to page 31, line 9; and from page 58, penultimate line, to page 63, line 20 of WO 98/22486. Other preferred metallocenes are the ones obtained from the bridged ligands listed from page 11, line 18, to page 14, line 13 of WO 99/24446
A further preferred class of transition metal organometallic catalyst compounds are late transition metal complex of formula (IX) or (X)
LaMaXapaxe2x80x83xe2x80x83(IX)
LaMaAaxe2x80x83xe2x80x83(X)
wherein Ma is a metal belonging to Group 8, 9, 10 or 11 of the Periodic Table of the Elements (new IUPAC notation);
La is a bidentate or tridentate ligand of formula (XI): 
wherein:
B is a C1-C50 bridging group linking E1 and E2, optionally containing one or more atoms belonging to Groups 13-17 of the Periodic Table;
E1 and E2, the same or different from each other, are elements belonging to Group 15 or 16 of the Periodic Table and are bonded to said metal Ma;
the substituents Ra1, equal to or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms); or two Ra1 substituents attached to the same atom E1 or E2 form a saturated, unsaturated or aromatic C4-C7 ring, having from 4 to 20 carbon atoms;
ma and na are independently 0, 1 or 2, depending on the valence of E1 and E2, so to satisfy the valence number of E1 and E2; qa is the charge of the bidentate or tridentate ligand so that the oxidation state of MaXapXaxe2x80x2s or MaAa is satisfied, and the compound (IX) or (X) is overall neutral;
Xa, the same or different from each other, are monoanionic sigma ligands selected from the group consisting of hydrogen, halogen, Ra, ORa, OSO2CF3, OCORa, SRa, xe2x80x94NRa2 and PRa2 groups, wherein the Ra substituents are linear or branched, saturated or unsaturated, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (new IUPAC notation), such as B, N, P, Al, Si, Ge, O, S and F atoms; or two Xa groups form a metallacycle ring containing from 3 to 20 carbon atoms; the substituents Xa are preferably the same;
pa is an integer ranging from 0 to 3, so that the final compound (IX) or (X) is overall neutral; and
Aa is a xcfx80-allyl or a xcfx80-benzyl group.
Non limiting examples of late transition metal complexes are those described in WO 96/23010, WO 97/02298, WO 98/40374 and J.Am.Chem.Soc. 120:4049-4050, 1998. Brookhart et al, J. Am. Chem. Soc. 1995, 117, 6414 and Brookhart et al, J. Am. Chem. Soc., 1996, 118, 267, Brookhart et al, J. Am. Chem. Soc. 1998, 120, 4049, Gibson et al, Chem. Commun. 1998, 849, WO 96/27439 and Chem. Ber./Recl. (1997), 130(3), 399-403.
It is a further object of the present invention a process for the polymerization of one or more olefins in the presence of a catalyst system as described above.
The organometallic compounds according to the invention exert good activities as cocatalysts in olefin polymerization process; Moreover, they are easy to prepare and do not lead to the release of undesired by-products after the metallocene activation. Further they are stable and produce stable catalyst compositions under polymerization conditions.
The organometallic compounds of the invention are easily prepared by reacting, in about stoichiometric amounts, a compound having the formula (I): 
wherein Ra, Rb, Rc and Rd are described above; with a Lewis acid of formula (II)
MtR13 xe2x80x83xe2x80x83(II)
wherein Mt and R1 are described above.
The reaction between said Lewis acid and the compound of formula (I) is preferably carried out in an aprotic solvent, even more preferably in a polar aprotic solvent (such as toluene, diethyl ether or CH2Cl2), at room temperature, the reaction can be carried out also in the presence of little amount of water, preferably equal to or less than one molar equivalent with respect to the Lewis acid. The acidity of the Lewis acid must be sufficiently high to induce the migration of a hydrogen from the N atom to the C atom in xcex1 or xcex2-position of the pyrrole ring.
The molar ratio between the organometallic compound (B) and the transition metal organometallic catalyst compound (A), calculated as the molar ratio between the metal Mt of the Lewis acid and the metal of the transition metal organometallic catalyst compound, preferably ranges from 10:1 to 1:10, more preferably from 2:1 to 1:2, and even more preferably is about 1:1.
According to the invention, component (B) can suitably comprise a mixture of two or more organometallic compounds of the invention. Moreover, component (B) can be used in combination with other compatible cocatalysts known in the state of the art, such as alumoxane compounds.
The catalyst system of the invention may also comprise one or more aluminum compounds of formula AlR103xe2x88x92zWz, acting as scavenger, wherein R10 can be C1-C10 alkyl, alkenyl or alkylaryl radicals, optionally containing one or more Si or Ge atoms, z is 0, 1 or 2 or a non integer number ranging from 0 to 2; U is chlorine, bromine or iodine atom and W is hydrogen, chlorine, bromine or iodine; non-limiting examples of aluminum compounds are trimethylaluminum (TMA), tris(2,4,4-trimethyl-pentyl)aluminum (TIOA), tris(2-methylpropyl)aluminum (TIBA), tris(2,3,3-trimethyl-butyl)aluminum, tris(2,3-dimethyl-hexyl)aluminum, tris(2,3-dimethyl-butyl)aluminum, tris(2,3-dimethyl-pentyl)aluminum, tris(2,3-dimethyl-heptyl)aluminum, tris(2-methyl-3-ethyl-pentyl)aluminum and tris(2-ethyl-3,3-dimethyl-butyl).
Another example of compound that can act as scavenger are alumoxane compounds containing at least one group of the type: 
wherein the R11 substituents, which may be the same or different, are described above. In particular, alumoxanes of the formula: 
can be used in the case of linear compounds, wherein n1 is 0 or an integer from 1 to 40 and the R15 substituents are defined as above, or alumoxanes of the formula: 
can be used in the case of cyclic compounds, wherein n2 is an integer from 2 to 40 and the R11 substituents are defined as above.
Examples of alumoxanes suitable as scavenger according to the present invention are metbylalumoxane (MAO), tetra-(isobutyl)alumoxane (TIBAO), tetra-(2,4,4-trimethylpentyl)alumoxane (TIOAO), tetra-(2,3-dimethylbutyl)alumoxane (TDMBAO) and tetra-(2,3,3-trimethylbutyl)alumoxane (TTMBAO).
Particularly interesting alumoxanes are those disclosed in WO 99/21899.
The catalyst system of the invention may be formed prior to its introduction into a polymerization reactor or in situ in the reactor, by contacting the above-described components (A), (B) and optionally (C).
According to an embodiment of the invention, components (A), (B) and optionally (C) are first contacted and then introduced into the reactor, wherein separately an aluminum compound AlR103xe2x88x92zWz, or an alumoxane has been introduced. Alternatively, components (A), (B) and optionally (C) and said aluminum compound AIR103xe2x88x92zWz or said alumoxane may be contacted together prior to their introduction into the reactor.
The catalysts of the present invention can be used on inert supports. This may be achieved by depositing said transition metal organometallic catalyst compound (A), or the product of the reaction thereof with the organometallic compound (B) and optionally with the alkylating agent (C), or said organometallic compound, and subsequently said transition metal organometallic compound before or after the optional treatment with said alkylating agent, on inert supports such as silica, alumina, styrene/divinylbenzene copolymers, polyethylene or polypropylene.
The thus obtained solid compound can be suitably used in gas phase polymerization.
The catalysts of the present invention can be used in the polymerization reactions of olefins. Therefore, according to a further object, the invention provides a process for the polymerization of one or more olefins comprising contacting one or more olefins under polymerization conditions in the presence of a catalyst system as described above.
Olefins which can be polymerized with the process of the present invention are, for instance, xcex1-olefins of formula CH2xe2x95x90CHR, wherein R is hydrogen or a C1-C20 alkyl radical.
The catalysts according to the present invention can be conveniently used in the homopolymerization of ethylene, in particular for the preparation of HDPE, and in the copolymerization of ethylene, in particular for the preparation of LLDPE. Suitable comonomers in ethylene copolymers are xcex1-olefins of formula CH2xe2x95x90CHRxe2x80x2, wherein Rxe2x80x2 is a linear, branched or cyclic C1-C20 alkyl radical or cycloolefins. Examples of such olefins are propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, allyl-cyclohexane, cyclopentene, cyclohexene, norbornene and 4,6-dimethyl-1-heptene.
Further suitable comonomers in said ethylene copolymers are polyenes, in particular conjugated or non-conjugated, linear or cyclic dienes, such as 1,4-hexadiene, isoprene, 1,3-butadiene, 1,5-hexadiene and 1,6-heptadiene.
When the organometallic compounds object of the present invention are used as cocatalyst in copolymerization of ethylene they generally produce a polymer having a higher molecular weight with respect to alumoxanes, in particular methylalumoxane.
The catalysts of the invention can be suitably used in propylene homopolymerization, in particular for the production of isotactic polypropylene.
Moreover, the catalysts of the invention can be suitably used in the preparation of elastomeric copolymers of ethylene with xcex1-olefins of formula CH2xe2x95x90CHRxe2x80x3, wherein Rxe2x80x3 is a C1-C10 alkyl radical, such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene; said copolymers may optionally contain minor proportions of units deriving from polyenes.
According to a further embodiment, the catalysts according to the present invention are used in the preparation of cycloolefin polymers. Monocyclic and polycyclic olefin monomers can be either homopolymerized or copolymerized, also with linear olefin monomers.
The polymerization processes of the present invention can be carried out in liquid phase, optionally in the presence of an inert hydrocarbon solvent, or in gas phase. Said hydrocarbon solvent can be either aromatic (such as toluene) or aliphatic (such as propane, hexane, heptane, isobutane, cyclohexane and 2,2,4-trimethylpentane).
The polymerization temperature preferably ranges from 0xc2x0 C. to 250xc2x0 C.; in the preparation of HDPE and LLDPE, it is preferably comprised between 20xc2x0 C. and 150xc2x0 C. and, more particularly between 40xc2x0 C. and 90xc2x0 C.; in the preparation of elastomeric copolymers, it is preferably comprised between 0xc2x0 C. and 200xc2x0 C., and more preferably between 20xc2x0 C. and 100xc2x0 C. The molecular weight of the polymers can be varied simply by varying the polymerization temperature, the type or the concentration of the catalyst components, or by using molecular weight regulators, such as hydrogen.
The molecular weight distribution can be varied by using mixtures of different metallocene complexes or by carrying out the polymerization in several stages which differ in the polymerization temperature and/or the concentrations of molecular weight regulator.
The polymerization yield depends on the purity of the transition metal organometallic catalyst compound (A) in the catalyst, therefore, said compound can be used as such or can be subjected to purification treatments before use.